Critically ill patients requiring mechanical ventilation are often victims of respiratory distress syndrome, status asthmaticus and pulmonary infections. Treatment of these and other severe respiratory conditions includes medications delivered directly to the lungs of the patient. Nebulized or aerosolized solutions are the preferred method of delivery of respiratory medication because the medicant is fragemented into small particles that are more efficiently deposited near sites of drug activity in the lung.
Nebulizers are well known in the art. Aerosolization of medications is performed by putting a liquid product in a chamber (nebulizer vial) that has a pressurized flow of gas through it. Utilizing the Bernoulli principle, liquid is drawn through an aspirator tube into the path of a high velocity gas and is fractured into a mist. The mist flows out of the nebulizer by inertial forces.
Current conventional aerosol drug therapy involves administering a finite quantity (dose) of medication deposited into the nebulizer vial and administered until the vial is empty. In normal practice, the period of delivery of each dose is measured in minutes or fractions of an hour. Depending upon the severity of the illness and the duration of activity of the medication, this process is repeated periodically at variable frequencies.
Such intermittent drug administration has the inherent results of (1) subjecting the patient to "peaks" and "valleys" of drug dosage effects, (2) requiring respiratory therapy personnel to periodically service the needs of the patient and nebulizer by measuring doses, disconnecting, filling and reconnecting the nebulizer and periodically monitoring the administration, and (3) disconnecting the patient from an attached ventilator during nebulizer service. Further, medication which is administered as a large volume, such as a surfactant, now requires large medicant flow volume through the nebulizer requiring frequent servicing and refilling of the nebulizer vial which intereferes with ventilator function.
In some cases, a significant porportion of the respiratory flow to the patient is through the nebulizer such as in the operational use of the VISAN nebulizer of Burroughs Wellcome Company. In the delivery of the medicant EXOSURF, up to half of the tidal volume flows through the nebulizing ports of the nebulizer to unite with the balance of the respiratory gas delivered directly from the ventilator in a Y-shaped junction in the flow path to the patient downstream from the nebulizer. In such delivery, the nebulizing gas is synchronized with the nebulizer such that nebulizing gas is delivered to the nebulizer only during the ventilatory inhalation cycle.
A nebulizer comprising a vial-like nebulizing chamber which comprises a two-position flow control valve assembly for accessibly draining and refilling the nebulizing chamber is disclosed in U.S. Pat. No. 4,805,609. While the valve assembly provides access for resupplying a medication dose while the nebulizing chamber remains in sealed relation with the nebulizer, such resupply is service intensive and limited to volumes containable by the nebulizing chamber.
Recent developments in respiration therapy involve aerosolization and delivery of the nebulized mist on a continuous basis over several hours. For example, an entire day's medication dosage is delivered at a constant rate over twenty-four hours, as opposed to conventionally delivering the same dosage for four separate aliquots at six hour intervals. Such delivery eliminates the "peak" and "valley" effects of the drug, reduces respiratory personnel support time, and also reduces the number of times critical medication/nebulizer interconnection is interrupted, thereby diminishing the potentially dangerous exposures of the patient to the effects of respiratory circuit contamination.
Delivery of medicated mist is both in combination with a ventilator and through masks, mouthpieces, and other voluntary mist inhalation apparatus.